In many fields of industry, science, and medicine, there is need for devices or systems capable of accurately metering and then blending individual concentrates of fluid to produce a desired mixture of same. Prior art procedures perform in a generally satisfactory manner when the proportionality between the several fluids to be metered and blended is constant. These prior art techniques are not satisfactory when the proportionality between the metered quantities is variable. The prior art methods are inadequate when three or more fluid quantities must be metered according to variable precise proportions.
Although the invention set forth herein may find application in other fields, the preferred embodiment herein described will be with respect to multiple fluid concentrate proportioning for preparation of dialysate for hemodialysis.
In preparation of dialysate for use in hemodialysis, a concentrate solution is diluted with the required amount of water. The concentrate is a solution containing predetermined amounts of various ions such as sodium, potassium, magnesium, calcium, acetate, and of dextrose. Patients' needs vary as to dialysis so that the dialysate must be tailored to the patient to contain the desired concentration of ionic materials. In order to provide such tailoring, varying quantities of two or more `standard` solutions containing the ions desired must be precisely blended. The present invention provides an accurate and convenient way for mixing controlled amounts of each of two or more concentrates with the required total amount of water to provide any desired amount of individual and collective ions in the resultant mixture.
As an illustration of the principles of the invention, consider a mix to contain both sodium and potassium ion in some predetermined and variably determinable ratio. One may start with two dialysate concentrates having in each the predetermined concentration of sodium ions. One concentrate will also include potassium ions. It is thus possible (within limits) to independently control the amounts and, therefore, the ratio of potassium and sodium ions in the final mixed dialysate. Control of this type is accurately and conveniently provided by the present invention by merely dialing in the desired concentrations of potassium and sodium ions on input switches. The system then automatically meters an amount of water and amounts of the two concentrate solutions in the proper proportion to give the desired dialysate makeup.